A. Field of the Invention
The present invention relates generally to a suspension system for use with optical technology based displacement detection, and more particularly, to control critical distances along the optical path for use with optical technology in an input device.
B. Description of the Related Art
Optical technology displacement detection is used in many contexts, including in optical input devices for a computer or other device that requires an input device. There are many different types of input devices, including a mouse, a trackball, a digital pen, and a joystick. There are significant advantages to using optical input devices over mechanical and opto-mechanical input devices. For example, mechanical or opto-mechanical input devices have mechanical components that are more susceptible to breakdown, wear out, or clogging. Optical devices having only solid-state components are less susceptible to such breakdown, wear out, or clogging.
Optical input devices use a displacement of an image to detect movement of the input device relative to surface, e.g., a table surface in the case of a mouse or a ball in the case of a trackball. Optical input devices use an imaging lens, a sensor, and a light source to detect movement of the input device. Typically the light source is a light emitting diode (LED). Conventionally, the LED is attached with a clip to a printed circuit board (PCB). The sensor is mounted on the PCB. The sensor is attached to the imaging lens. There are two dimensions that are important to control to ensure the quality of the image. One important distance is the distance between the moving surface, e.g. table or ball, and the lens. The second important distance is the distance between the lens and the sensor. Conventional optical devices do not precisely control the distance between the moving surface and the lens.
Additionally, alignment of the imaging lens, the sensor, and the LED is critical. The alignment has a direct impact on the surface illumination and therefore on image quality. If the distance from the lens to the surface is not correct, oblique lighting creates a shift of the lighted area, which then does not match the area seen by the sensor, resulting in a partially dark image. Good surface illumination and good image quality are essential to an efficient optical system in an input device.
There are several reasons the alignment of the imaging lens, the sensor, and the LED is not always good. In conventional systems, critical optical dimensions are a result of many different parts stacked on top of each other creating an accumulation of errors. A critical optical dimension is a dimension that is critical for the optical system to create a sharp image of the surface, e.g., the table or the ball on the sensor; usually it is the path between the sensor and the surface. In the conventional optical path described above, there are errors introduced as a result of each part, e.g., the bottom of a case for the input device, the PCB, the clip, the LED, the sensor, and the imaging lens. This chain of parts is referred to as a chain of critical dimensions.
Another factor that leads to errors in alignment is that in conventional systems, positioning elements are built on the input device case to reduce the number of parts, cost and assembly time. When manufacturing the case, the highest priority is a cosmetic aspect of the product. Precise dimensions of the case assembly is a lesser priority, however, it can effect the alignment and the dimensions, as described above. Conventional systems use plastic that is chosen for cosmetic appearance and cost, not for mechanical precision. Consequently, the plastic used for the case adds to the chain of critical dimensions and is not a precision part.
Additionally, there are inherent errors introduced by using injected plastic parts. In conventional systems, most of the parts used are made of injected plastic. Injected plastic parts warp over time due to time and variations in temperature. Larger plastic pieces tend to warp more than smaller ones. The bottom of the case of the input device is made from a large piece of injected plastic. It is then a main cause of errors. In some conventional systems, this warping can degrade the performance of the input device or make it stop working completely.
There are several problems with conventional systems. One significant problem with conventional systems is the precise position of the imaging lens relative to the surface. This problem is caused by the chain of dimensions described above. Each part introduces more errors due to the tolerance of the particular connection between any two parts. Another problem is that a small error on the distance to the target can move a lighted spot away from its ideal position.
Another problem of conventional systems is electro static discharges (ESD). Sensitive electronics should be protected from these discharges because they can disturb their function or destroy the components. One conventional solution to the problem of ESD is to increase the distance between internal circuits and the outside world. A conventional solution is to use interleaving structures that make the path of a potential arc of discharge longer. A longer arc is less likely to have a discharge. Thus, there is a higher trigger voltage. The trigger voltage is the voltage difference required to trigger an ESD. To be effective, the trigger voltage should be higher than the specified ESD performance of the product.
Another problem of conventional systems is that conventional input devices are not waterproof. When a device is not waterproof, it can be damaged by spilled drinks or food or moisture entering the device as a result of humid climates.
What is needed is a system and method to precisely position the optical module relative to the imaged surface for use in an optical system that overcomes the above described problems and limitations.
The present invention provides a suspension system that reduces the number of critical parts. Thus, errors introduced in the chain of critical dimensions are reduced. One embodiment of the present invention provides an optical module that includes a sensor, a lens, a LED, and a LED clip correctly positioned together. Another aspect of the present invention suppresses the effects of the dimension errors in the bottom of the case from the critical dimensions chain. Yet another aspect of the present invention improves ESD immunity by providing a completely sealed structure for the bottom of the case. Finally, one embodiment of the present invention provides a waterproof-type barrier for the case.
One embodiment of the present invention flexibly couples the optical module to the bottom of the case. The bottom of the case can have an opening. The optical module can be positioned above the opening in the case such that the light illuminates a surface and the optical module protrudes through the opening. The surface can be a table or a mouse pad for an optical mouse or a ball for an optical trackball. One embodiment of the present invention uses an articulating arm to flexibly couple the optical module to the bottom of the case. The arm positions the optical module above the opening in the case. Optionally, a spring can also be used to apply a force on the optical module in the direction of the surface such that the optical module is in contact with the surface. Contact points can be part of the optical module and their position relative to the lens is precise because there is only one part in between. Thus, significantly reducing the accumulation of errors affecting the distance between the surface and the lens. When the optical module is in contact with the surface, the image is much sharper. In one embodiment, a flexible membrane can be attached to the bottom of the case over the opening in the case. The membrane is also attached to the optical module and acts to flexibly suspend the optical module over the surface. In one embodiment, the membrane is transparent to the wavelength or wavelengths of light used by the optical module so that light can pass through the membrane without having a hole in the membrane. In another embodiment, a hole can be made in the membrane to allow light to pass through.
Contact points can prevent the optical module from wearing out as a result of friction on the surface. Contact points can be any shape or size and are attached to the optical module or the membrane. The contact points can be made out of a low friction material or a hard material.
The present invention eliminates errors introduced by the bottom of the case because the optical module is flexibly suspended over an opening in the case. Therefore, even if there are imperfections in the bottom of the case or if the surface has irregularities, the imperfections will not alter the position of the optical module and therefore the illumination and the sharpness of the image. The position of the optical module is not dependent on the bottom of the case.
Additionally, a membrane can provide ESD protection. In one embodiment, the entire case can be lined with a membrane. In that embodiment, the case is protected from ESD because the membrane provides a barrier for discharge. Moreover in this embodiment, the membrane also provides a waterproof-type barrier.
The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter.